Receiver desensitization (“desense”), or degradation of receiver sensitivity, may result from noise interference from a nearby transmitter. In particular, when two radios are close together with one transmitting on the uplink and the other receiving on the downlink, the feedback from the transmitter may be picked by the receiver. As a result, the received signals may become corrupted and difficult or impossible to decode. Further, feedback from the transmitter can be detected by a power monitor that measures the receive signal, which would cause the mobile device to falsely determine the presence of a cell site. In particular, receiver desense may present a challenge in multi-radio devices, such as devices configured with multiple subscriber identity modules (SIMs), due to the necessary proximity of transmitter and receiver.
In general, mobile device radio receivers may have filters to reduce interference from a simultaneous transmit signal. In order to be effective, a transmit filter needs to be positioned in the radio circuitry after the signal is amplified, but that requires a filter that can handle high power levels, and such filters are expensive. Consequently, protocols for mobile communication systems are designed to mitigate desense without the need to use a filter in the transmitter, such as by avoiding simultaneous transmit and receives (such as UTRAN TDD, E-UTRAN TDD), by sufficiently separating the frequency domain between transmit and receive signals (such as GSM, UTRAN FDD, E-UTRAN FDD), etc.).
Dual-SIM mobile devices have become increasing popular because of their flexibility in service options and other features. One type of dual-SIM mobile device, a dual-SIM dual active (DSDA) device, allows simultaneous active connections with the networks corresponding to both SIMs. DSDA devices typically have separate transmit/receive chains associated with each SIM. As such, previous communication system designs are inadequate to prevent desense in devices that have two or more of these radio access technologies operating within the same device at the same time, such as in DSDA mobile devices.